This invention relates to the field of pumps, and more particularly, to a heart pump useable for pumping blood.
Various different heart pumps have been used to pump blood through a human body. Pulsatile blood flow, simulating actual blood flow as provided by the heart, is more easily produced using a piston type heart pump. However, pulsatile blood flow may also be produced by a centrifugal heart pump powered by an electric inverter. Certain heart pumps have been designed for use as artificial or substitute hearts to be either implanted within a body, or mounted subcutaneously to pump blood throughout the body.
As an alternative to the substitute artificial heart, various cardiac assist pumps, designed to be mounted subcutaneously in conjunction with a weak existing heart, have been developed. The purpose of assist devices is to alleviate and/or minimize stress in a patient's natural heart without sacrificing overall pumping ability. The centrifugal heart pumps which have been used as cardiac assist devices include miniature motors which are mounted intravascularly between the left ventricle and aorta artery, between ventricles, within the heart itself or within the femoral aorta artery.
For example, U.S. Pat. No. 4,105,016 to Donoran discloses a heart pump which is mountable in parallel relationship with a ventricle and is run at a constant speed. The pump automatically operates when the pressure within the ventricle reaches a predetermined value. U.S. Pat. Nos. 4,265,712 and 4,846,156 to Wampler disclose a high capacity intravascular blood pump utilizing percutaneous access which may be inserted into the heart through the femoral artery and driven via a flexible cable from an external power source. Also, U.S. Pat. No. 4,173,796 to Jarvik discloses a circulatory assist device which may be mounted between the left ventricle and right ventricle. These pumps are essentially centrifugal pumps which utilize conventional impellers and/or rotors to pump blood.
Since these centrifugal cardiac assist pumps typically require bearings and seals, it is desirable to develop a heart pump which minimizes the use of such bearings or seals and therefore provides greater reliability during use. Also, since intravascular heart pumps are designed to minimize stress on the heart, it is desirable to utilize a heart pump which can operate for a maximum period of time without failure.
One potential problem with centrifugal rotor and impeller type pumps may be that they damage blood cells as the blood cells pass through the rotor or impeller. The extreme pressure differential across rotors or impellers may cause the explosive decompression and cavitation, etc of blood cells. It is therefore desirable to develop a heart pump which will minimize damage to blood cells being pumped therethrough.
Another problem with conventional heart pumps including heart assist devices is that their pumping rates cannot be varied adequately to mimic a healthy heart. As the heart becomes weakened, its ability to increase its pumping rate becomes diminished. Typical induction motors used as heart assist devices are inherently difficult to modulate so as to precisely control the rotation thereof. It is therefore desirable to achieve a heart pump which will be capable of producing a pulsatile flow and also be capable of creating a variable pumping rate.
The pump disclosed in U.S. Pat. No. 4,688,998 includes a magnetically suspended and rotated impeller pump which may be connected between the heart and the aortic arch. The impeller is magnetically suspended and rotated and a valve may be included as part of the impeller to prevent reverse flow if the pump is used as a ventricle assist device. Another magnetic-type heart assist device, disclosed in U.S. Pat. No. 4,779,614 to Moise, may allow for greater blood flow. This axial flow blood pump utilizes neodymium-boron-iron rotor magnets which allow a substantial gap between the static motor armature and the rotor. Therefore, greater blood flow may be induced as compared to conventional magnetically suspended rotor impeller pumps.
One potential problem with both magnetic and other conventional types of heart pumps including assist devices, is that the flow of blood therethrough crosses an intense magnetic field. The full effects of the magnetic field upon blood cells are unknown. However, the effects of low level electro-magnetic radiation upon the human body have been questioned. Therefore, heart pumps which allow blood to flow through intense magnetic and/or electromagnetic fields may not be desirable.
Accordingly, it is desirable to achieve a heart pump in which blood flowing therethrough does not intercept a magnetic field. It is also desirable to develop a centrifugal subcutaneously mountable heart pump and/or heart assist device which may be precisely controlled so as to more adequately mimic the performance of a normal heart and create variable pulsatile flow. Moreover, it is desirable to develop a heart pump and assist device, which utilizes a synchronous AC motor while minimizing damage to blood cells pumped therethrough. The pump should be capable of being intravascularly attached between a ventricle of the heart and an artery.